Hermetic Compressor

ABSTRACT

A hermetic compressor has a bipolar permanent magnet motor where permanent magnet ( 124 ) is disposed in rotor core ( 123 ). Hollow bore ( 131 ) is disposed at the end on the compressing element ( 105 ) side of rotor core ( 123 ), and main bearing ( 111 ) extends into bore ( 131 ). The thickness of rotor core ( 123 ) is longer than that of stator core ( 126 ), thereby widening the magnetic path of rotor core ( 123 ). The magnetic flux amount generated in rotor core ( 123 ), which is conventionally insufficient due to existence of bore ( 131 ), increases, the loss decreases, and the efficiency increases.

TECHNICAL FIELD

The present invention relates to a hermetic compressor used for afreezing cycle in a refrigerator freezer or the like.

BACKGROUND ART

Recently, regarding a hermetic compressor used for a freezing apparatusin a refrigerator freezer or the like, the increase of the efficiency isdesired for reducing consumed power, and the downsizing is desired forincreasing the capacity efficiency of the refrigerator freezer.

Japanese Patent Unexamined Publication No. 2001-73948 (hereinafterreferred to as “document 1”), for example, discloses a conventionalbipolar permanent magnet motor having a built-in permanent magnet in arotor as an motor element, instead of an induction motor, in order toimprove the efficiency.

A conventional hermetic compressor is described hereinafter withreference to the accompanying drawings.

FIG. 10 is a longitudinal sectional view of the conventional hermeticcompressor described in document 1. As shown in FIG. 10, hermeticcontainer 1 accommodates motor element 4 formed of stator 2 and rotor 3and compressing element 5 driven by motor element 4. Hermetic container1 hermetically encloses motor element 4 and compressing element 5.

Lubricating oil 6 is reserved in hermetic container 1. Shaft 10 has mainshaft 11 to which rotor 3 is fixed and eccentric shaft 12 formedeccentrically with respect to main shaft 11. Cylinder block 14 hassubstantially cylindrical compressing chamber 15 and main bearing 17that is made of aluminum base material, namely non-magnetic material.Piston 19 is inserted into compressing chamber 15 of cylinder block 14which is slidable back and forth in compressing chamber 15, and iscoupled to eccentric shaft 12 through connector 20.

Motor element 4 is a bipolar permanent magnet motor that is formed ofthe following elements:

-   -   stator 2 where a wire is wound on stator core 25 made of a        laminated magnetic steel sheet; and    -   rotor 3 where permanent magnet 27 is built in rotor core 26 made        of a laminated magnetic steel sheet.        End plate 28 for protection for preventing permanent magnet 27        from dropping is fixed to rotor core 26.

Hollow bore 31 is disposed at an end on a side of rotor core 26 facingcompressing element 5, and main bearing 17 extends inside hollow bore31.

Operations of the hermetic compressor having this configuration aredescribed hereinafter. Rotor 3 of motor element 4 rotates shaft 10, anda rotation of eccentric shaft 12 is transmitted to piston 19 viaconnector 20, thereby reciprocating piston 19 in compressing chamber 15.By the reciprocation of piston 19, refrigerant gas is sucked from acooling system (not shown) into compressing chamber 15, compressed, andthen discharged to the cooling system again.

The flow and loss of the magnetic flux during the rotation of rotor 3are described hereinafter. Since main bearing 17 is made of thenon-magnetic material, magnetic attraction force does not work betweenthe inner periphery of bore 31 and main bearing 17, and hence torqueloss does not occur. Further, since main bearing 17 is made of thenon-magnetic material, the magnetic flux from permanent magnet 27 is notattracted to main bearing 17, and hence most of the magnetic flux passesonly through rotor core 26. Therefore, core loss (especially, eddycurrent loss) hardly occurs in main bearing 17, and the efficiency canbe increased.

In the conventional configuration, however, magnetic path cannotpenetrate through main shaft 11 made of the non-magnetic material. Theregion through which the magnetic flux can pass in bore 31 of rotor core26 is therefore small. Therefore, only partially narrow magnetic pathcan be formed, the magnetic resistance is large, and the magnetic fluxamount near bore 31 is smaller than that in the case having no bore 31.Therefore, the loss becomes large disadvantageously.

When the bore is not formed in the bearing structure in order to reducethe loss in bore 31, main bearing 17 cannot extend into bore 31 formedin rotor core 26. In other words, vertical overlap between bore 31 andmain bearing 17 is eliminated, and hence rotor 3 moves to the sideopposite to compressing element 5 by the depth of bore 31. As a result,the height of hermetic container 1 increases by the depth of bore 31disadvantageously.

SUMMARY OF THE INVENTION

In the hermetic compressor of the present invention, the motor elementis a bipolar permanent magnet motor formed of a stator and a rotor thathas a built-in permanent magnet in a rotor core. A hollow bore isdisposed at an end on a compressing element side of the rotor core, anda main bearing extends inside the bore.

The axial length of the rotor core is longer than that of a stator coreof the stator. The magnetic path of the rotor core can be made wide, sothat the magnetic flux amount generated in the rotor core increases, theloss decreases, and the efficiency of the motor element increases. Thestructure provides a wide magnetic path is provided to smooth flow ofmagnetic flux by the permanent magnet.

The main shaft may be made of magnetic material. In this case, the mainbearing of magnetic material and a shaft that are disposed inside thebore work as the magnetic path, so that the magnetic flux amount(conventionally, insufficient) generated in the rotor increases, and theloss decreases. The structure provides a wide magnetic path provided tosmooth flow of magnetic flux by the permanent magnet.

In the hermetic compressor of the present invention, the magnetic pathinside the bore can be formed without increasing the height of thehermetic container, so that the magnetic flux amount generated in therotor increases, the loss decreases, and the efficiency can beincreased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a hermetic compressor inaccordance with exemplary embodiment 1 of the present invention.

FIG. 2 is an axial sectional view of a part having no bore in a rotor inaccordance with exemplary embodiment 1.

FIG. 3 is an axial sectional view of a part having a bore in the rotorin accordance with exemplary embodiment 1.

FIG. 4 is a longitudinal sectional view of a hermetic compressor inaccordance with exemplary embodiment 2 of the present invention.

FIG. 5 is a longitudinal sectional view of a hermetic compressor inaccordance with exemplary embodiment 3 of the present invention.

FIG. 6 is an enlarged sectional view of an essential part of thehermetic compressor in accordance with exemplary embodiment 3.

FIG. 7 is an axial sectional view of a part having a bore in a rotor inaccordance with exemplary embodiment 3.

FIG. 8 is a characteristic diagram of magnetic flux density inside thebore in the rotor in accordance with exemplary embodiment 3.

FIG. 9 is a characteristic diagram of coefficient of performance of thehermetic compressor in accordance with exemplary embodiment 3.

FIG. 10 is a longitudinal sectional view of a conventional hermeticcompressor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the hermetic compressor of the present invention, lubricating oil isreserved in a hermetic container, and a motor element and a compressingelement are also accommodated in the hermetic container. The compressingelement has a shaft including an eccentric shaft and a main shaft, and amain bearing for pivoting the main shaft. The motor element is a bipolarpermanent magnet motor that is formed of a stator and a rotor. The rotorhas a built-in permanent magnet in a rotor core. A hollow bore isdisposed at an end on a compressing element side of the rotor core, andthe main bearing extends inside the bore. The thickness, namely axiallength, of the rotor core is longer than that of the stator core of thestator. The magnetic path of the rotor core can be made wide, so thatthe magnetic flux amount in the rotor core increases and the lossdecreases. Conventionally, the magnetic flux amount is insufficient dueto the narrow magnetic path by the bore. The thickness of the rotor corethat does not directly affect the height of the hermetic container ismade long, so that the height of the hermetic container is notincreased. Therefore, the hermetic compressor can be downsized andlightened, the cost can be reduced, and the efficiency can be increased.

In the hermetic compressor of the present invention, both axial ends ofthe rotor core may be disposed outside both axial ends of the statorcore, respectively. The magnetic centers of the stator and the rotorsubstantially match with each other, so that axial electromagnetic forcehardly occurs, and electromagnetic force acting on the rotor can beeffectively converted to torque for rotating the shaft. Therefore, theefficiency is further increased.

In the hermetic compressor of the present invention, the axial length ofthe permanent magnet may be shorter than that of the rotor core. Themagnetic flux generated by the permanent magnet hardly leaks from anaxial end of the rotor core to the outside, so that the material cost ofthe permanent magnet can be reduced without largely reducing aneffective magnetic flux amount. The cost can be further reduced.

The hermetic compressor of the present invention may have theconfiguration where the axial length of the permanent magnet is shorterthan that of the rotor core and the permanent magnet lies on the sideopposite to the bore of the rotor. The magnetic flux generated by thepermanent magnet is mainly generated in a wide part having no bore inthe rotor core, so that a wide magnetic path can be formed, and thematerial cost of the permanent magnet can be reduced without largelyreducing an effective magnetic flux amount of the permanent magnet. Thecost can be further reduced.

In the hermetic compressor of the present invention, the bipolarpermanent magnet motor used as the motor element may be a self-startingpermanent magnet synchronous motor that has the following elements:

-   -   many conductor bars of a cage conductor for start on the outer        periphery of the rotor core; and    -   a rotor having a plurality of permanent magnets buried in its        inner periphery.        A synchronous motor having high efficiency can be employed, and        the efficiency of the hermetic compressor can be increased.

In the hermetic compressor of the present invention, the permanentmagnet may be a rare-earth magnet. The rear-earth magnet can provide astrong magnetic force, so that the motor can be downsized and lightened,and the hermetic compressor can be downsized and lightened.

In the hermetic compressor of the present invention, the main bearingmay be made of magnetic material. The main bearing and shaft made of themagnetic material inside the bore work as a magnetic path, so that themagnetic flux amount generated in the rotor increases beyond the loss byeddy current generated in the main bearing, and the loss decreases.Therefore, the efficiency of the motor element increases and hence theefficiency of the hermetic compressor can be increased.

In the hermetic compressor of the present invention, the main bearingmay be made of a sintered iron base material or a casting of iron basematerial. The bearing can be made of inexpensive iron base material andcan be formed unitarily with the cylinder block, so that the cost can bereduced.

In the hermetic compressor of the present invention, the depth of thebore (or axial length of the bore) may be ⅓ of the thickness of therotor core or more. Extension of the main bearing made of the magneticmaterial into the bore compensates for insufficiency in magnetic flux inthe rotor. Here, the insufficiency is caused by small thickness of thepart having no bore in the rotor core. Therefore, in this case, theheight of the hermetic container can be made smaller than that in thecase where a rotor core has the same thickness and no bore is disposed,and the efficiency can be increased.

-   In the hermetic compressor of the present invention, the clearance    between an outer peripheral edge of the bore and an outer peripheral    edge of the main bearing may be set at 0.5 to 3 mm. The outer    peripheral surface of the bore corresponds to an inside surface of a    cylindrical bore of the rotor core. The magnetic resistance in the    clearance between the bore and the main bearing decreases, a strong    magnetic path is formed, the leaking magnetic flux decreases, and    the magnetic flux amount increases, so that the efficiency can be    further increased.

Exemplary embodiments of the present invention are described hereinafterwith reference to the accompanying drawings. The present invention isnot limited to these exemplary embodiments. For clearly showing eachelement in the drawings, longitudinal or lateral contraction scale ofsome elements is extended.

Exemplary Embodiment 1

FIG. 1 is a longitudinal sectional view of a hermetic compressor inaccordance with exemplary embodiment 1 of the present invention. FIG. 2is an axial sectional view of a part having no bore in a rotor inaccordance with exemplary embodiment 1. FIG. 3 is an axial sectionalview of a part having a bore in the rotor in accordance with exemplaryembodiment 1.

In FIG. 1, FIG. 2 and FIG. 3, hermetic container 101 reserveslubricating oil 102 and accommodates motor element 103 and compressingelement 105 driven by motor element 103. Compressing element 105 hasshaft 110 including eccentric shaft 106 and main shaft 107 and mainbearing 111 for pivoting main shaft 107. Cylinder block 112 has asubstantially cylindrical compressing chamber 113. Main bearing 111 madeof aluminum-base material, namely non-magnetic material, is fixed tocylinder block 112. Piston 114 is inserted into compressing chamber 113of cylinder block 112 which can slide back and forth in compressingchamber 113, and is coupled to eccentric shaft 106 through connector115.

In exemplary embodiment 1, motor element 103 is a bipolar self-startingpermanent magnet synchronous motor that is formed of stator 121 androtor 125. Rotor 125 has built-in permanent magnet 124 in rotor core123. The thickness, namely axial length, of rotor core 123 is longerthan that of stator core 126 of stator 121. End plate 127 for protectionfor preventing permanent magnet 124 from dropping is fixed to rotor core123. Many conductor bars 128 disposed in rotor core 123 andshort-circuit rings 129 positioned at both axial ends of rotor core 123are unitarily molded by aluminum die casting, thereby forming a cageconductor for start.

Both axial ends of rotor core 123 are disposed outside both axial endsof stator core 126, respectively. In other words, the upper end of rotorcore 123 is higher than that of stator core 126, and simultaneously thelower end of rotor core 123 is lower than that of stator core 126.Hollow bore 131 is disposed at the end on the compressing element 105side of rotor core 123, and main bearing 111 extends into bore 131.

Here, bore 131 is described. Rotor core 123 has cylindrical through hole133, and shaft 110 is inserted into through hole 133. Bore 131 is anannular recessed part disposed in the upper part of through hole 133. Inother words, bore 131 is a step having a diameter larger than that ofthrough hole 133. Therefore, the lower end of main bearing 111 isaccommodated in bore 131, and hence inserted into the gap between shaft110 and rotor core 123.

Permanent magnet 124 is a magnet plate made of Neodymium Iron Boronferromagnetic material, namely a rare-earth magnet. Permanent magnet 124is formed of permanent magnets 124A, 124B, 124C and 124D, and they arearranged as shown in FIG. 2. A pair of permanent magnets 124A and 124Bof the same polarity are faced to each other around shaft 110 at apredetermined angle and a predetermined interval. While, a pair of otherpermanent magnets 124C and 124D of the same polarity are faced to eachother around shaft 110 at a predetermined angle and a predeterminedinterval. All of permanent magnets 124A, 124B, 124C and 124D are buriedin parallel with the axis of rotor core 123. The pair of permanentmagnets 124A and 124B of the same polarity form one rotor magnetic pole,and the pair of other permanent magnets 124C and 124D of the samepolarity also form one rotor magnetic pole. Therefore, whole rotor 125forms two rotor magnetic poles. For preventing short circuit of magneticfluxes of adjacent permanent magnets 124A and 124C or of adjacentpermanent magnets 124B and 124D, barrier 132 for preventing shortcircuit of magnets is formed. Barrier 132 is a hole in which aluminumdie casting of non-magnetic material is filled.

A refrigerant used in the compressor is a hydrocarbon refrigerant or thelike, namely a natural refrigerant having low global warming potentialsuch as R134a or R600a having zero ozone depleting coefficient, and isused in combination with lubricating oil having high compatibility.

Operations and actions of the hermetic compressor having theabove-mentioned configuration are described hereinafter.

Rotor 125 of motor element 103 rotates shaft 110, and a rotation ofeccentric shaft 106 is transmitted to piston 114 via connector 115,thereby reciprocating piston 114 in compressing chamber 113. Thus,refrigerant gas is sucked from a cooling system (not shown) intocompressing chamber 113, is compressed, and is discharged to the coolingsystem again.

Next, flow of the magnetic flux of permanent magnet 124 is conceptuallydescribed with arrow lines in FIG. 2 and FIG. 3. The flow of themagnetic flux in the part having no bore 131 in rotor core 123 isdescribed in FIG. 2. The magnetic flux coming from permanent magnet 124Aor permanent magnet 124B travels through the central part of rotor core123 and is attracted into permanent magnet 124C or permanent magnet124D, respectively.

While, the flow of the magnetic flux in bore 131 in rotor core 123 isdescribed in FIG. 3. The magnetic flux coming from permanent magnet 124Aor permanent magnet 124B cannot travel through main bearing 111 made ofaluminum-base material of non-magnetic material, so that the flux doesnot travel into hollow bore 131 and diffracts to proximity of a voidformed of the outer periphery of main bearing 111 and the innerperiphery of bore 131. Therefore, the magnetic path in this part isusually apt to become narrow and insufficient.

In exemplary embodiment 1, the axial length of rotor core 123 is longerthan that of stator core 126 of stator 121, so that a wide magnetic pathcan be formed in the axial direction of rotor core 123. As a result, themagnetic flux amount (conventionally, insufficient) in rotor core 123increases, and the loss decreases. As discussed above, motor element 103of exemplary embodiment 1 has a wide magnetic path, and the flow of themagnetic flux by permanent magnet 124 is smooth.

Since the axial length of rotor core 123 that does not directly affectthe height of hermetic container 101 is made long, the height ofhermetic container 101 is not increased. The height of hermeticcontainer 101 decreases by the depth (or axial length) of bore 131comparing with the case having no bore 131, and hence hermetic container101 can be downsized and lightened.

Since both axial ends of rotor core 123 are disposed outside both axialends of stator core 126, respectively, so that the magnetic centers ofstator 121 and rotor 125 substantially match with each other. Therefore,axial electromagnetic force hardly occurs, the electromagnetic forceacting on rotor 125 can be effectively converted to the torque forrotating shaft 110, and hence the efficiency is further increased.

As a result, the hermetic compressor can be downsized and lightened, thecost can be reduced, and the efficiency can be increased.

When a hollow part is disposed in the shaft for oil supply, the magneticpath is apt to be insufficient similarly to the case having bore 131.Therefore, the actions by the above-mentioned configuration work furthereffectively, and a similar effect can be obtained.

Exemplary Embodiment 2

FIG. 4 is a longitudinal sectional view of a hermetic compressor inaccordance with exemplary embodiment 2 of the present invention. Inexemplary embodiment 2, elements similar to those in exemplaryembodiment 1 are denoted with the same reference marks, and the detaildescriptions of those elements are omitted.

In FIG. 4, hermetic container 101 reserves lubricating oil 102 on itsbottom, and accommodates motor element 201 and compressing element 105driven by motor element 201. Compressing element 105 has shaft 110including eccentric shaft 106 and main shaft 107 and main bearing 111for pivoting main shaft 107. Cylinder block 112 has a substantiallycylindrical compressing chamber 113, and main bearing 111 made ofaluminum-base material, namely non-magnetic material. Piston 114 isinserted into compressing chamber 113 of cylinder block 112 which canslide back and forth in compressing chamber 113, and is coupled toeccentric shaft 106 through connector 115.

In exemplary embodiment 2, motor element 201 is a bipolar self-startingpermanent magnet synchronous motor that is formed of stator 202 androtor 206. Rotor 206 has built-in permanent magnet 205 in rotor core203. The thickness, namely axial length, of rotor core 203 is longerthan that of stator core 210 of stator 202 in exemplary embodiment 2.End plate 211 for protection for preventing permanent magnet 205 fromdropping is fixed to rotor core 203.

Hollow bore 212 is disposed at the end on the compressing element 105side of rotor core 203, and main bearing 111 extends into bore 212. Theaxial length of permanent magnet 205 is shorter than that of rotor core203. Permanent magnet 205 is fixed to the lower side of rotor core 203having no bore 212. In other words, permanent magnet 205 covers theregion having no bore 212 in the axial direction of rotor 206 (heightdirection in FIG. 4). Rotor core 203 has cylindrical through hole 133,and shaft 110 is inserted into through hole 133 with the first diameter.Bore 212 is an annular recessed part disposed in the upper part ofthrough hole 133. In other words, bore 212 is a step having the seconddiameter larger than the first diameter of through hole 133. Therefore,the lower end of main bearing 111 is accommodated in bore 212, and henceinserted into the gap between shaft 110 and rotor core 203. Permanentmagnet 205 covers a region of rotor core 203 having the second diameter.

Permanent magnet 205 is a magnet plate made of Neodymium Iron Boronferromagnetic material, namely a rare-earth magnet. The configuration ofpermanent magnet 205 is similar to those of FIG. 2 and FIG. 3. In otherwords, two permanent magnets 205 form one rotor magnetic pole, and fourpermanent magnets 205 form two rotor magnetic poles in whole rotor 206.Many conductor bars that are disposed in rotor core 203 andshort-circuit rings 213 that are positioned at both axial ends of rotorcore 203 are unitarily molded by aluminum die casting, thereby forming acage conductor for start. For preventing short circuit of magneticfluxes of adjacent permanent magnets 205, barrier 132 for preventingshort circuit of magnets is formed, and aluminum die casting is filledinto the hole in barrier 132.

A refrigerant used in the compressor is a hydrocarbon refrigerant or thelike, namely a natural refrigerant having low global warming potentialsuch as R134a or R600a having zero ozone depleting coefficient, and isused in combination with lubricating oil having compatibility.

The operations of the hermetic compressor having this configuration aredescribed hereinafter.

Rotor 206 of motor element 103 rotates shaft 110, and a rotation ofeccentric shaft 106 is transmitted to piston 114 via connector 115,thereby reciprocating piston 114 in compressing chamber 113. Thus,refrigerant gas is sucked from a cooling system (not shown) intocompressing chamber 113, compressed, and then discharged to the coolingsystem again.

Next, flow of the magnetic flux of permanent magnet 205 is conceptuallydescribed. The flow of the magnetic flux in the part having no bore 212in rotor 206 is similar to that in FIG. 2. The magnetic flux coming frompermanent magnet 205 travels through the central part of rotor core 203.While, the flow of the magnetic flux in the part which has bore 212 inrotor 206 is similar to that in FIG. 3. The magnetic flux coming frompermanent magnet 205 cannot travel through hollow bore 212, because mainbearing 111 made of non-magnetic material exists in bore 212. Therefore,the magnetic flux diffracts to proximity of the void formed of the outerperiphery of main bearing 111 and the inner periphery of bore 212. Themagnetic path in this part is therefore apt to become narrow andinsufficient.

However, since the axial length of permanent magnet 205 is shorter thanthat of rotor core 203, the magnetic flux generated by permanent magnet205 hardly leaks from the axial end of rotor core 203 to the outside.Therefore, the material cost of permanent magnet 205 can be reducedwithout largely reducing the effective magnetic flux amount. Asdiscussed above, motor element 103 of exemplary embodiment 2 has a widemagnetic path, and the flow of the magnetic flux by permanent magnet 205is smooth.

Permanent magnet 205 is disposed in the vertical direction of rotor 206and at a lower position opposite to the upper position having bore 212.The vertical overlap between permanent magnet 205 and bore 212 isminimized. In this configuration, the magnetic flux by permanent magnet205 occurs in the large part having no bore 212 in rotor core 203, sothat a magnetic path wider than the size of permanent magnet 205 can beformed, the material cost of permanent magnet 205 can be reduced withoutlargely reducing the effective magnetic flux amount of permanent magnet205. Therefore, the efficiency is increased and simultaneously the costis reduced.

Permanent magnet 205 is a rare-earth magnet. The rare-earth magnet canapply a strong magnetic force, so that the motor can be downsized andlightened, and the hermetic compressor can be downsized and lightened.

Therefore, the size and the weight can be further reduced, the cost canbe reduced, and the efficiency can be increased.

When a hollow part such as a passage for oil supply is disposed in mainshaft 107 of shaft 110, the magnetic path is apt to be insufficientsimilarly to the case having bore 212. Therefore, the operations by theabove-mentioned configuration work further effectively, and a similareffect can be obtained.

Exemplary Embodiment 3

FIG. 5 is a longitudinal sectional view of a hermetic compressor inaccordance with exemplary embodiment 3 of the present invention. FIG. 6is an enlarged sectional view of an essential part of the hermeticcompressor in accordance with exemplary embodiment 3. FIG. 7 is an axialsectional view of a part having a bore in a rotor in accordance withexemplary embodiment 3. FIG. 8 is a characteristic diagram betweenmagnetic flux density inside the bore and the clearance between thediameter of the bore and the outer diameter of the main bearing, in therotor in accordance with exemplary embodiment 3. FIG. 9 is a comparativecharacteristic diagram of coefficient of performance C.O.P of thehermetic compressor. In exemplary embodiment 3, elements similar tothose in exemplary embodiment 1 are denoted with the same referencemarks, and the descriptions of those elements are simplified.

As shown in FIG. 5, FIG. 6 and FIG. 7, hermetic container 101 reserveslubricating oil 102 inside, and accommodates motor element 103 andcompressing element 105. Compressing element 105 has shaft 110 includingeccentric shaft 106 and main shaft 107 and main bearing 111 for pivotingmain shaft 107. Cylinder block 112 has a substantially cylindricalcompressing chamber 113, and main bearing 111 made of casting ofiron-based material, namely magnetic material. Piston 114 is insertedinto compressing chamber 113 of cylinder block 112 slidably back andforth, and is coupled to eccentric shaft 106 through connector 115.

Motor element 103 is a bipolar self-starting permanent magnetsynchronous motor that is formed of stator 121 and rotor 306. Rotor 306has built-in permanent magnet 305 in rotor core 303. Thin end plate 311for protection for preventing permanent magnet 305 from dropping isfixed to rotor core 303. Many conductor bars 308 that are disposed inrotor core 303 and short-circuit rings 309 that are positioned at bothaxial ends (in other words, upper and lower ends) of rotor core 303 areunitarily molded by aluminum die casting, thereby forming a cageconductor for start.

Hollow bore 131 is disposed at the end on the compressing element 105side of rotor core 303, and main bearing 111 extends into bore 131.

As shown in FIG. 6, the thickness of rotor core 303 is denoted with L,the inner diameter and depth of bore 131 are denoted with D1 and M,respectively, and the outer diameter of main bearing 111 is denoted withD2. In exemplary embodiment 3, depth M is set ⅓ of thickness L or more,and clearance G between the outer periphery of main bearing 111 and theinner periphery of bore 131 is set at 0.5 to 3 mm. Here, G=(D1−D2)/2.

Permanent magnet 305 is a magnet plate made of Neodymium Iron Boronferromagnetic material, namely a rare-earth magnet. Permanent magnet 305is formed of permanent magnets 305A, 305B, 305G and 305D, and they arearranged as shown in FIG. 7. A pair of permanent magnets 305A and 305Bof the same polarity are faced to each other around shaft 110 at apredetermined angle and a predetermined interval. While, a pair of otherpermanent magnets 305C and 305D of the same polarity are faced to eachother around shaft 110 at a predetermined angle and a predeterminedinterval. All of permanent magnets 305A, 305B, 305C and 305D are buriedin parallel with rotor core 303. The pair of permanent magnets 305A and305B of the same polarity form one rotor magnetic pole, and the pair ofother permanent magnets 305C and 305D of the same polarity form onerotor magnetic pole. Therefore, whole rotor 306 forms two rotor magneticpoles. For preventing short circuit of magnetic fluxes of adjacentpermanent magnets 305A and 305C or of adjacent permanent magnets 305Band 305D, barrier 132 for preventing short circuit of magnets is formed.Barrier 132 is a hole hilled with aluminum die casting.

A refrigerant used in the compressor is a hydrocarbon-based refrigerantor the like, namely a natural refrigerant having low global warmingpotential such as R134a or R600a having zero ozone depletingcoefficient, and is used in combination with lubricating oil havingcompatibility.

Operations and actions of the hermetic compressor having theabove-mentioned configuration are described hereinafter.

Rotor 306 of motor element 103 rotates shaft 110. A rotation ofeccentric shaft 106 is transmitted to piston 114 via connector 115,thereby reciprocating piston 114 in compressing chamber 113. Thus,refrigerant gas is sucked from a cooling system (not shown) intocompressing chamber 113, is compressed, and is discharged to the coolingsystem again.

Flow of the magnetic flux of permanent magnet 305 is conceptuallydescribed with arrow lines in FIG. 7. FIG. 7 shows the flow of themagnetic flux in bore 131 in rotor core 303. As shown in FIG. 7, themagnetic flux coming from permanent magnet 305A or permanent magnet 305Btravels through the clearance between the outer periphery of mainbearing 111 and the inner periphery of bore 131, main bearing 111, andshaft 110, and is attracted into permanent magnet 305C or permanentmagnet 305D, respectively.

At this time, main bearing 111 extending into bore 131 does not rotate,so that the travel of the magnetic flux causes eddy current loss.However, lost torque due to eddy current caused on the outer diameter ofmain bearing 111 is relatively smaller than the torque of the motor initself generated on the outer periphery of rotor 303. That is becausethe distance from the rotating shaft is short and hence the forceworking as the braking torque is weak. While, main bearing 111 made ofmagnetic material and shaft 110 form a magnetic path, so that themagnetic flux amount generated in rotor 306 increases. This effectincreases with increase in depth M of bore 131. As a result, theinfluence of the torque loss is small relatively. Therefore, theincrease in magnetic flux amount generated in rotor 306 reduces the lossto increase the efficiency of motor element 103, and hence theefficiency of the hermetic compressor can be increased. As discussedabove, motor element 103 of exemplary embodiment 3 has a wide magneticpath, and the flow of the magnetic flux by permanent magnet 305 issmooth.

Since depth M of bore 131 is set ⅓ of thickness L or more in exemplaryembodiment 3 and is extremely deep, especially the magnetic flux amountgenerated in rotor 306 increases, the increasing effect of theefficiency is remarkable, and the whole height of the compressor is keptextremely low.

Main bearing 111 can be made of inexpensive casting or sinteredmaterial, and can be formed unitarily with cylinder block 112, so thatthe cost can be reduced.

As shown in FIG. 8, when clearance G (where, G=(D1−D2)/2) between bore131 and main bearing 111 is increased, the magnetic flux density insidebore 131 decreases. However, when clearance G is increased larger than 3mm, the magnetic flux density hardly decreases. When main bearing 111and shaft 110 are used as a magnetic path through which the magneticflux passes, the clearance up to 3 mm is considered to be appropriate.While, in consideration of the processing accuracies of the outerperiphery of main bearing 111 and the inner periphery of bore 131,clearance G of 0.5 to 3 mm is most preferable and effective. By applyingthe above conditions, therefore, the magnetic resistance decreases, astrong magnetic path is formed, the leaking magnetic flux decreases, themagnetic flux amount increases, and the efficiency increases further.

In starting, a large current flows to generate torque in conductor bars308. The magnetic force by built-in permanent magnet 305 works asbraking torque in starting, so that a large starting torque is required.In exemplary embodiment 3, conductor bars 308 can be elongated and thestarting torque can be increased, so that the starting property is goodand high efficiency can be obtained.

More preferably, permanent magnet 305 is formed of a rare-earth magnet.The rear-earth magnet can apply a strong magnetic force, so that themotor can be downsized and lightened, and the hermetic compressor can bedownsized and lightened.

Therefore, the size and the weight can be further reduced, the cost canbe reduced, and the efficiency can be increased.

In exemplary embodiment 3, main bearing 111 made of casting of iron-basematerial is formed unitarily in cylinder block 112. A configurationwhere main bearing 111 made of iron-base sintered material is fixed alsoproduces a similar advantage.

Increase in efficiency of the hermetic compressor in exemplaryembodiment 3 is described hereinafter.

In FIG. 9, the vertical axis shows characteristics of coefficients ofperformance C.O.P (W/W) of the hermetic compressors of the conventionalart and exemplary embodiment 3. Here, R600a is used as the refrigerant,and the operation frequency in reciprocating the piston is 50 Hz. Theoperation temperature condition is close to the operation condition in arefrigerator, the evaporation temperature is −25° C., and condensationtemperature is 55° C.

As is clear from the result in FIG. 9, in the hermetic compressor ofexemplary embodiment 3, the C.O.P is largely improved comparing with theconventional hermetic compressor, and the efficiency is increased.

INDUSTRIAL APPLICABILITY

In the hermetic compressor of the present invention, the magnetic fluxamount in the rotor core increases to decrease the loss, the size andweight can be reduced, and the efficiency can be increased. Therefore,the hermetic compressor can be applied to an air conditioner or arefrigerator freezer.

1. A hermetic compressor comprising: a hermetic container; a motorelement accommodated in the hermetic container; and a compressingelement that is accommodated in the hermetic container and driven by themotor element, wherein the compressing element has a shaft including aneccentric shaft and a main shaft, and a main bearing for pivoting themain shaft, the motor element is a bipolar permanent magnet motor thathas a stator and a rotor, the rotor having a built-in permanent magnetin a rotor core, a hollow bore is formed at an end on the compressingelement side of the rotor core, and a wide magnetic path is provided tosmooth flow of magnetic flux by the permanent magnet.
 2. The hermeticcompressor according to claim 1, wherein axial length of the rotor coreis longer than axial length of a stator core of the stator, hence thewide magnetic path is provided to smooth the flow of the magnetic fluxby the permanent magnet.
 3. The hermetic compressor according to claim2, wherein both axial ends of the rotor core are disposed outside bothaxial ends of the stator core, respectively.
 4. The hermetic compressoraccording to claim 2, wherein axial length of the permanent magnet isshorter than axial length of the rotor core.
 5. The hermetic compressoraccording to claim 2, wherein axial length of the permanent magnet isshorter than axial length of the rotor core, and the permanent magnetcovers a region having no bore in the axial direction of the rotor. 6.The hermetic compressor according to claim 2, wherein, the rotor corehas a cylindrical through hole having a first diameter into which theshaft is inserted, the bore is a cylindrical recessed part that isformed in the upper part of the through hole and has a second diameterlarger than the first diameter, the permanent magnet has an axial lengthshorter than the axial length of the rotor core, and covers a region ofthe first diameter in the rotor in an axial direction of the rotor core.7. The hermetic compressor according to claim 1, wherein the mainbearing is made of magnetic material, and the wide magnetic path isprovided to smooth the flow of the magnetic flux by the permanentmagnet.
 8. The hermetic compressor according to claim 7, wherein themain bearing is one of a casting and a molded product that is made ofiron-based sintered material.
 9. The hermetic compressor according toclaim 7, wherein axial length of the bore is ⅓ of axial length of therotor core or more.
 10. The hermetic compressor according to claim 7,wherein a clearance between an peripheral surface of the bore and anouter peripheral surface of the main bearing is 0.5 to 3 mm.
 11. Thehermetic compressor according to claim 1, wherein the motor element is aself-starting permanent magnet synchronous motor, the motor element hasmany conductor bars of a cage conductor for start on the outer peripheryof the rotor core, and the permanent magnet is disposed in the innerperipheral side of the conductor bars.
 12. The hermetic compressoraccording to claim 1, wherein the permanent magnet is a rare-earthmagnet.
 13. The hermetic compressor according to claim 8, wherein axiallength of the bore is ⅓ of axial length of the rotor core or more. 14.The hermetic compressor according to claim 8, wherein a clearancebetween an peripheral surface of the bore and an outer peripheralsurface of the main bearing is 0.5 to 3 mm.
 15. The hermetic compressoraccording to claim 2, wherein the motor element is a self-startingpermanent magnet synchronous motor, the motor element has many conductorbars of a cage conductor for start on the outer periphery of the rotorcore, and the permanent magnet is disposed in the inner peripheral sideof the conductor bars.
 16. The hermetic compressor according to claim 7,wherein the motor element is a self-starting permanent magnetsynchronous motor, the motor element has many conductor bars of a cageconductor for start on the outer periphery of the rotor core, and thepermanent magnet is disposed in the inner peripheral side of theconductor bars.
 17. The hermetic compressor according to claim 2,wherein the permanent magnet is a rare-earth magnet.
 18. The hermeticcompressor according to claim 7, wherein the permanent magnet is arare-earth magnet.